Thanks, the tree is doing well.
I wouldn't have repotted the tree in summer if it was doing well. But the fact is that it was so rootbound that watering was proving difficult. So it wasn't taking up any of the liquid feed I use - they just ran off. In addition it is a very well established tree that has had many strong seasons in my garden, so I know it can handle this work.
A week after repotting I applied some chicken manure pellets - hate them but they work. The tree greened-up nicely and the mildew became easier to control. Those are factors that suggest the tree is healthier than before the re-pot. Still never sure, but I think it was the right decision. Here are smoe current pics:
20210720_102658 by BrendanR2012, on Flickr
20210720_102705 by BrendanR2012, on Flickr
